I'm a pretty big fan of DN, and no fan of Gearbox, but on this -- considering the details I know or understand -- I can't really side with 3D Realms/Interceptor on this. Up until now I had assumed this new DN game was produced by Gearbox, or they had special permission from Gearbox to do it.
If they don't, they shouldn't, and Gearbox has every right to lay claim to their own property.
If they don't, they shouldn't, and Gearbox has every right to lay claim to their own property.